The need exists for apparatus capable of accurate temperature measurement and display in environments which are hostile to measurement apparatus, or which are not amenable to instrumentation because they are moving or inaccessible. In a number of industrial processes it is important to measure the temperature of the material being processed, in both absolute and relative terms, and to be able to display the measured values in a way which is immediately useful to operators for purposes of warning and fault correction.
In the past, thermocouples, thermoplies, thermally-sensitive resistors, semiconductor junctions and similar devices have been employed, in contact with the measured object, to measure temperatures in a variety of applications. The use of such devices suffers from the drawback that physical attachment to or immersion in the object or substance being measured is required. While many applications do not suffer other than inconvenience from this requirement, in other applications it is necessary to abandon the attempt to measure temperature unless a non-contacting temperature sensor can be employed.
In the field of industrial process controls, the inability to measure the temperature of many continuous motion processes without first bringing the process to a halt is a major cause of waste of time, material and capital.
For example, in coated paper manufacturing processes, it is desirable to measure the temperature of the paper as it moves from one point to another. Since the paper is manufactured in a continuous ribbon, and is moving at relatively high speeds, access to the paper for measurement and quality control purposes is problematic. At the same time, if waste is to be avoided, the temperature of the paper must be known at various states of the process. In the coating process, molten coating material is applied continuously to the moving base paper. If the temperature of the paper base and coating material combination is too high at the time of application, the coating material penetrates too deeply causing the surfaces of the paper to be rough. On the other hand, if the coating material is too cold, the coating becomes too thick and, consequently, wasteful of materials. In extreme cases, the coating will not bond the base material if it is applied at temperatures which are too cold. Accordingly, it is necessary to precisely measure the temperature of the paper as it is being coated in order to determine whether the process is within acceptable temperature limits. Generally, it is not the average temperature of a segment of the paper which is determinative of its quality, rather it is the temperature of a small section or spot. The temperature of small spots of abnormally high or low temperatures may be indicative of satisfactory or unsatisfactory processing of an entire production batch. Detection of a spot having abnormal temperature is difficult with average reading temperature measuring equipment but failure to detect abnormalities and to correct the process is extremely costly. Entire batches are frequently rendered unuseable due to the inability of existing equipment to make this measurement.
Remote measurement of the moving paper ribbon is evidently required since attachment of a temperature transducer is not possible. However, equipment for remote temperature measurement having sufficiently fast response times and capable of covering an area as large as that required for paper manufacturing, while still being capable of detecting small segments of anomolous temperatures, has heretofore not been available.
Similar problems exist in processing of plastic films, tapes, foils and other laminar or ribbon-shaped materials.
A somewhat different application exists in the metal refining industry. In refining metals by process of electrolysis, vast areas of tanks containing a metal bearing electrolyte and cathode and anode plates are employed. The plates are series or parallel connected together, immersed in the electrolyte, and a current is passed through the plates resulting in electrolytic deposition of refined metal on the plates. Many pairs of plates are employed in each electrolyte bath. Malfunction of the plates by shorting together in common and highly costly since not only is the refinement process terminated at shorted plates, but power is dissipated and energy consumed without benefit being realized. The obvious difficulty in detecting and correcting malfunctions is that, short of electrical testing performed on each set of plates, a time-consuming and costly process which requires shutdown of a complete tank, no effective way presently exists for determining which plates are malfunctioning. Since many pairs of plates exist within one tank, instrumentation of each plate pair is impractical. However, the performance of each tank is reflected in the temperatures which are produced by the process and, given the proper apparatus, a survey of temperature can quickly locate the bath in which malfunctioning plates are present by detecting an anamolous average temperature. Since many factors such as ambient temperature, current supplied and electrolyte condition affect the temperature of the electrolyte bath, a measurement of absolute temperature will not be dispositive as to the presence or absence of abnormalities in any given tank. However, determination of comparative or relative temperatures followed by isolation of those tanks which display a significant deviation from the norm will quickly lead to the malfunctioning tank. Further isolation of the malfunction down to the level of individual plate pairs can then be accomplished.
Malfunctioning shorted plates within the electrolyte bath are reflected in a lower than normal temperature in their immediate vicinity in the case of series-connected plates, and higher than normal temperatures in their immediate vicinity in the case of parallel-connected plates. A radiometric sensor having sufficiently fine temperature resolution can provide isolation of the malfunctioning plates by simply interdicting a thermal isolator between each plate pair and the radiometer and noting the change in average apparent bath temperature as each plate pair's contribution is removed from the average. Normally functioning plates will, of course, have similar temperatures and will have similar effects when their contributions are removed from the radiometer's field of view. Malfunctioning plates will, on the other hand, have an abnormal effect on the apparent average bath temperature and therefore may be readily isolated. Use of the same apparatus is possible for both isolation of tanks containing malfunctioning plates and isolation of individual plate pairs within the bath if the apparatus is capable of sufficiently fine resolution of temperatures within a given temperature range, and simultaneous display and comparison of a multiplicity of sensor inputs due to the need for locating one sensor at each electrolyte bath and for the need to make comparative as well as absolute temperature measurements.